The molecular genetics of the lens are being investigated through the study of Delta-crystallin. This protein and its gene and mRNA are being investigated at the levels of gene organization, expression, and nucleotide sequence. There are two genes for Delta-crystallin in the chicken genome. The genes are located together in one 30 Kb (kilobase) locus and are 4.2 Kb apart. They are oriented in the same direction for transcription. cDNAs corresponding to only the first gene have been found, suggesting that mRNA from gene 1 is much more abundant than from gene 2. It remains to be shown that gene 2 produces a functional mRNA. A full-length cDNA clone has been obtained and sequenced. The mRNA for Delta-crystallin is 1572 bases in length (excluding the Poly(A) tail) and encodes a 447 amino acid polypeptide. The promoters from genes 1 and 2 have been sequenced and compared. There are several structural differences that might account for the differences in transcriptional activity of genes 1 and 2.